The present invention relates to a semiconductor integrated switching circuit for switching input-output signal in high frequency circuit, more particularly, to the one for controlling and reducing higher harmonic component caused by non-linearity of the semiconductor integrated switching circuit.
Conventionally, as this kind of circuit, for example, single pole 4 through switching circuit Sc employed in a dual-band mobile phone shown in FIG. 5 is well known.
The description of the circuit in the prior art will be given with referring to the FIG. 5. The single pole 4 trough switching circuit is configured as a semiconductor integrated circuit comprising four field effect transistors TR1, TR2, TR3, TR4 and attached between an antenna 71 and following high frequency circuits LNA1, PA1, LNA2, PA2 in a so-called dual-band mobile phone which can transmit and receive at two different radio frequencies.
In this term, LNA1 is a receiving front end for one band of two different frequencies, i.e. band A, PA1 is a transmitting amplification unit of band A, LNA2 is a receiving front end for the other band of two different frequencies, i.e. band B, PA2 is a transmitting amplification unit of band B.
In such configuration, in case of receiving of the band A, while control voltage VA is set to given value so as to make TR1 xe2x80x9conxe2x80x9d state, control voltage VB, VC and VD are to be set to given values so as to keep TR2 to TR4 xe2x80x9coffxe2x80x9d state (Refer to FIG. 6). In case of keeping either of transistor TR2 trough TR4 xe2x80x9conxe2x80x9d state, each xe2x80x9conxe2x80x9d/xe2x80x9coffxe2x80x9d state of the transistor TR1 through TR4 shall be controlled by control voltage VA through VD.
In the conventional circuit, a nonlinear characteristic of the field effect transistor cause higher harmonics thereby the higher harmonics shall be output from the antenna 71 with the transmitting signal. However as for the electromagnetic wave from the antenna 71, there is a need to control the higher harmonic level to satisfy the demand due to the radio law for restricting the output level and the tolerance of unnecessary frequency components.
As a method for controlling the higher harmonic level, there is a method of attaching a band pass filter (BPF) of 2 bands between the single pole 4 through switching circuit Sc and the antenna 71.
However, there is a case where the frequency of band B is set to be even numbered multiple of band A, for example, 0.9 GHz and 1.8 GHz as two bands of the dual-band mobile phone. In such case, there is a problem the band pass filter (BPF) is useless because the second order harmonic of 0.9 GHz conforms to the band B of 1.8 GHz, thereby passes through the filter.
Moreover, even in the passing band of the filter, it may cause a loss in a passing signal, therefore while it may lowers the transmitting level at the transmission, and also deteriorates the receiving sensitivity due to the lower level of the receiving signal at the reception.
Furthermore, since the mobile phone is required to be downsized, it is very difficult to give room for adding a filter between the single pole 4 through switching circuit Sc and the antenna 71. Therefore, it is not practical to control and reduce higher harmonic with the filter.
The present invention is directed to solve said problem, and provide a semiconductor integrated switching circuit which controls the generation of unnecessary higher harmonic while reducing passing loss.
To attain the object of the invention, a semiconductor integrated switching circuit according to the present invention comprises a common input-output terminal, input/output terminals, switching elements for connecting terminals each of which interposed between the common input-output terminal and respective one of the input/output terminals, a ground terminal for grounding, a series resonance circuit having a resonance frequency set to be a higher harmonic of the fundamental frequency that passes trough one of the switching elements, and a switching element for the series resonance circuit. The series resonance circuit and the switching element for the series resonance circuit are connected in series and interposed between the common input-output terminal and the ground terminal. The control voltage applied to said one of the switching elements is commonly applied to the switching element for the series resonance circuit.
In the semiconductor integrated switching circuit having such configurations, a switching element for connecting terminals through which a signal including higher harmonic to be removed passes and a switching element for series resonance circuit are applied with same control voltage and turn on simultaneously. Therefore, the series resonance circuit is electrically connected between the common input-output terminal and the ground so that higher harmonic included in the signal is diverted into the ground through the series resonance circuit. That is, only the signal having same frequency as resonance frequency of the series resonance circuit is removed and other signal could pass through the switching element for connecting terminals without any influences of the series resonance circuit.
Accordingly, it becomes possible to provide a semiconductor integrated switching circuit in which the generation of unnecessary higher harmonic is prevented and the loss of passing signal is minimized.